(1) Field of Invention
This invention relates to a method for treating an olefin polymer after polymerization, and more specifically, to a method which by a simple operation, can markedly reduce the amount of an electron donor remaining in an olefin polymer after polymerization, the electron donor being an ingredient of a catalyst used in the polymerization and constituting the main cause of an offensive odor which the resulting polymer gives off.
More specifically, this invention relates to a method for treating an olefin polymer, which comprises contacting an olefin polymer obtained by polymerizing an olefin in the presence of a catalyst composed of (A) a highly active transition metal compound, (B) an organoaluminum compound and (C) a carbonyl- or Si-containing electron donor, with (D) an organometallic compound of a metal of Groups I to III of the periodic table after the polymerization.
In the present application, the term "polymerization" may sometimes denote both homopolymerization and copolymerization, and the term "polymer", both a homopolymer and a copolymer.
(2) Discussion of Prior Art
An olefin polymer obtained by using an old Ziegler catalyst, for example a catalyst comprising a transition metal compound such as titanium trichloride obtained by reducing titanium tetrachloride with metallic aluminum, an organometallic compound, etc., and an organoaluminum compound contains an unnegligible amount of a catalyst residue attributed to the transition metal or aluminum. To remove the catalyst residue, the polymer must be subjected to a deashing treatment using a lower alcohol, for example.
It is known on the other hand to polymerize an olefin in the copresence of an electron donor as a third component in addition to the aforesaid transition metal compound and the organoaluminum compound in order to regulate the activity of the catalyst and control the stereospecificity or molecular weight of the resulting polymer. In recent years, the development of various types of highly active transition metal compounds having the ability to form an olefin polymer in an amount of at least about 5,000 g per millimole of the transition metal has made it possible to omit the aforesaid deashing treatment. Although the deashing treatment can be omitted in preparing an olefin polymer by polymerizing an olefin in the presence of a catalyst composed of the aforesaid highly active transition metal compound, organoaluminum compound and electron donor, it was newly found that the electron donor remains in the resulting polymer in an amount on the order of about 10 ppm or more, and causes the trouble of giving off an offensive odor in subsequent handling, for example during film formation or injection molding.
No proposal, however, has been made in the past for removing this new trouble. Since a polymer obtained by using a conventional Ziegler catalyst composed of a transition metal compound and an organoaluminum compound contains an unnegligible amount of a metal-containing catalyst residue as stated hereinabove, it has previously been important and essential to remove the catalyst residue, and this removal has usually been performed by using a lower alcohol. As an improvement of the treatment for removing such a metal-containing catalyst residue, there is known a method which comprises first treating the polymer with an alkylaluminum chloride or a boron halide in the presence of a liquid hydrocarbon, and then treating the resulting product with a lower alcohol (see Japanese Patent Publication No. 14787/60 corresponding to British Pat. No. 849,085). This method contemplates the removal of the metal-containing catalyst residue in two steps, and the patent exemplifies the use of an old Ziegler catalyst of low activity composed of titanium trichloride and triethyl aluminum. The patent fails to disclose anything about the use of a highly active transition metal compound as a catalyst ingredient, and also the use of an electron donor as a joint catalyst component. Furthermore, the patent naturally does not give any description or suggestion about the aforesaid new trouble attributed to the electron donor remaining in an olefin polymer which is obtained by polymerizing an olefin in the presence of a catalyst composed of the highly active transition metal compound, organoaluminum compound and electron donor and which requires no treatment for removing a catalyst residue; much less a solution to such a problem.
The present inventors made extensive investigations in order to develop a method which can give a solution to this new problem effectively by an industrially easy operation. These investigations have led to the discovery that when an olefin polymer obtained by polymerizing an olefin in the presence of a catalyst composed of a highly active transition metal compound, an organoaluminum compound and an electron donor is treated after the polymerization with an organometallic compound of a metal of Groups I to III of the periodic table, the electron donor remaining in the polymer in an amount of about 10 ppm or more and constituting the main cause of the trouble of offensive odors can be decreased drastically, and thus, the aforesaid trouble can be removed effectively by an easy treating operation.
It is an object of this invention therefore to provide a treating method which offers a solution to the new technical problem associated with the use of a highly active catalyst.
The above and other objects and advantages of this invention will become apparent from the following description.